Highly Luminescent Heavier Main Group Analogues of Boron-Dipyrromethene

Article abstract of DOI:10.1021/jacs.9b03235

The preparation and photophysical properties of two heavier main group element analogues of boron-dipyrromethene (BODIPY) chromophores are described. Specifically, we have prepared dipyrrin complexes of dichlorogallate (GADIPY) or phenylphosphenium (PHODIPY) units. Whereas cationic PHODIPY is labile, decomposing to a phosphine over time, GADIPY is readily prepared in good yield as a crystalline solid having moderate air- and water-stability. Crystallographically characterized GADIPY displays intense green photoluminescence (λ_em = 505 nm, φ_em = 0.91 in toluene). These inaugural heavier main group element analogues of BODIPY offer a glimpse into the potential for elaboration to a panoply of chromophores with diverse photophysical properties.

Full text of DOI:10.1021/jacs.9b03235

Communication
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Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Highly Luminescent Heavier Main Group Analogues of Boron-
Dipyrromethene
Wang Wan,† Mayura S. Silva,† Colin D. McMillen,† Stephen E. Creager,†,‡ and Rhett C. Smith*,†,‡
†Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
‡Center for Optical Materials Science and Engineering Technology, Clemson University, Anderson, South Carolina 29625, United
States
S
* Supporting Information
second row elements by heavier main group elements can have
ABSTRACT: The preparation and photophysical proper-
ties of two heavier main group element analogues of
boron-dipyrromethene (BODIPY) chromophores are
described. Specifically, we have prepared dipyrrin
complexes of dichlorogallate (GADIPY) or phenyl-
phosphenium (PHODIPY) units. Whereas cationic
PHODIPY is labile, decomposing to a phosphine over
time, GADIPY is readily prepared in good yield as a
crystalline solid having moderate air- and water-stability.
Crystallographically characterized GADIPY displays in-
dramatic impacts on a molecule’s optical and electronic
properties,16−20 so pursuing heavier main group dipyrrin
complexes has attracted some attention. Although some
mono(diiminato)gallium complexes21−24 and bis- or tris-
(dipyrrin) complexes (Chart 1)25,26 have been characterized,
the mono(dipyrrin)gallium complexes (direct analogues of
BODIPY) have not been observed. Whereas BODIPY
chromophores generally have a photoluminescent quantum
efficiency (Φ) >60%, making them outstanding fluorescent
probes, the oligo(N-chelating ligand) gallium complexes
exhibit very poor Φ (<3%, Table 1).
tense green photoluminescence (λem = 505 nm, Φem
=
0.91 in toluene). These inaugural heavier main group
element analogues of BODIPY offer a glimpse into the
potential for elaboration to a panoply of chromophores
with diverse photophysical properties.
Table 1. Select Photophysical Properties
e
Φ (%)
λmax (nm)
λem (nm)
Eg (eV)
a
a
a
BODIPY
Ga(NacNac)Cl2
Ga(msdpm)3
80
<1
2.4
505
516
2.9
ND
ND
3.0
3.0
3.1
b
b
382
ND
528
c
c
c
496
he boron-dipyrromethene (BODIPY) chromophores
(Chart 1) have attracted broad multidisciplinary interest
GADIPY (CH2Cl2)
GADIPY (Toluene)
82
91
80
494
497
467
501
505
510
T
d
PHODIPY
Chart 1. Selected Structure of BODIPY and Coordination
a
b
c
Complexes of Gallium(III) with N,N′-Bidentate Ligands
BODPY data are as reported in CH2Cl2.1 In THF. In hexane.
d
Data are for the equilibrium mixture in CH2Cl2 that produced the
e
31P NMR shown in Figure S3 of the SI. From DFT calculations in
vacuo.
The established preparation of BODIPY is very low yielding,
and so requires column chromatographic purification.27 The
instability of heavier main group element-halogen bonds to
chromatographic purification on silica/alumina precludes the
isolation of direct BODIPY analogues via this route, possibly
explaining their absence from the literature. Recent insightful
improvements to the traditional BODIPY synthesis by
Thompson’s group27 have inspired the current effort to
explore heavier main group analogues of BODIPY. In the
improved procedure, Thompson reported that isolation of the
dipyrrinato lithium salt (1, Scheme 1) prior to installation of
the boron center leads to near quantitative yields of BODIPY
chromophores, foregoing the need for chromatographic
purification. We hypothesized that the high yield and attendant
purification by crystallization using this protocol would
facilitate ready access to the desired heavier main group
owing to their advantageous and tunable combination of
photophysical features. Although many fluorescent dipyrrinato
complexes have been reported,2 including Zn(II),3−6 Mg-
(II),7,8 Ir(III),9 Cu(II),10 Al(III),11 PO2,12,13 and Sn(II)14,15
complexes, it is striking that direct BODIPY analogues
composed of dipyrromethane adducts of other heavier main
group elements have not been elucidated. Substitution of
Received: March 25, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/jacs.9b03235
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
similarly generated. Cyclic voltammetry (Figure S8 in the SI)
for GADIPY reveals a reversible oxidation at 1.30 V and a
partially reversible reduction at −1.10 V. These features are
analogous to those observed in BODIPY at +1.22 and −1.24 V,
respectively.37
Scheme 1. PHODIPY and GADIPY Are Readily Prepared
from the Lithium Dipyrrin Salt
Whereas successful preparation of GADIPY demonstrates
the success of the proposed strategy for preparing heavier main
group analogues of BODIPY, the ability to install other main
group fragments should also allow access to dipyrrin complexes
having properties inaccessible to their borane analogues. Given
the significant differences in biolocalization for neutral versus
charged probes, a readily prepared, inherently cationic
BODIPY analogue could be a valuable cellular imaging
agent, specifically as a mitochondria-targeting therapeutic.38−40
An inherently cationic dipyrrin-phosphenium complex was
therefore a tantalizing target. Although phosphenium frag-
ments are unstable, there are several approaches41−43 for their
generation in situ that allow them to be trapped by N,N-
chelating ligands (i.e., P1, Chart 1).44−50 In the current case,
phenylphosphenium was generated by reaction of PhPCl2 and
TMSOTf. Reaction of the [PhPOTf]+ fragment so generated
with 1 produced phenylphosphenium (PHODIPY) having a
31P NMR spectroscopic shift (65.5 ppm) consistent with
previously reported N,N-chelate phosphenium triflate com-
plexes (70.9 ppm).51 Unlike GADIPY, however, PHODIPY is
labile even under an inert atmosphere. When the solvent is
removed from the reaction mixture and the crude material is
immediately analyzed, 81% of the phosphorus-bearing species
is present as PHODIPY. The decomposition products are
tentatively assigned as phosphine 2 (HRMS, M + 1 calcd for
C32H36N4P, 507.2678; found, 507.2690) and insoluble material
(Scheme 2). The 31P NMR chemical shift of 2 (48.8 ppm) is
analogues. Several fragments that are pseudoisolobal to borane
were considered for this initial study. Dichlorogallate
(GADIPY) (Scheme 1) was the most obvious target because
gallium is a heavier congener of boron that will yield analogous
bonding geometry and should exhibit photophysical properties
similar to the BODIPY analogues. Furthermore, GADIPY
could have an advantage over BODIPY for biomedical
applications because gallium compounds are useful for
biomedical radiolabeling.28−35
Our initial effort to prepare GADIPY involved reaction of 1
with GaCl3, analogous to how the boron analogue is prepared.
This reaction gave a mixture of products, likely due to the high
reactivity of GaCl3. Reaction of [PPh4][GaCl4]36 with 1,
however, gave GADIPY in 42% yield as an analytically pure
crystalline solid. Crystals of GADIPY are stable at room
temperature in the air, and were suitable for single crystal X-ray
diffraction. The X-ray structure of GADIPY (Figure 1 and
Scheme 2. Decomposition of PHODIPY
consistent with that of other bis(N-aryl)phenylphosphines
such as bis(N-indolyl)phenylphosphine (48.6 ppm).52 Exten-
sive efforts to isolate PHODIPY from the mixture were
unfortunately unsuccessful, and photophysical properties
reported in Table 1 are for the mixture under nitrogen.
The photophysical properties (Table 1 and Figure 2) of
GADIPY in CH2Cl2 are quite similar to those of the direct
BODIPY analogue (Chart 1, X = Cl, R = H). Compared to
BODIPY, GADIPY exhibits only slight blue shifts of 11 nm in
λmax and 15 nm in λem, while the Φ values for the two are
identical within error (both ∼80%). Depending on the solvent,
the Φ of GADIPY is as high as 91% (in toluene).
The mixture of PHODIPY and 2 (Scheme 2) produces the
absorption and emission spectra represented by the black
traces in Figure 2. The absorption spectrum of PHODIPY
exhibits a small band at 511 nm of intensity consistent with
∼20% contribution of 2, and a peak at 467 nm attributable to
PHODIPY. Independently prepared dipyrrin phosphines53
such as 2 exhibit very low Φ (<1%), consistent with other
chromophore-derivatized phosphines,54−56 so photolumines-
cence from the mixture is attributable exclusively to
PHODIPY. This is further confirmed by noting only very
Figure 1. Single-crystal X-ray diffraction structure of GADIPY. The
image is an ORTEP rendering of 50% probability ellipsoids. H atoms
are omitted for clarity.
Table 2) reveals the tetrahedral, BODIPY-like geometry about
Ga (full structural details are provided in the SI). The bond
lengths and angles about Ga in GADIPY are quite comparable
to those observed in Ga(NacNac)Cl2 (Chart 1).21 Other
GADIPY complexes such as EtGADIPY (Scheme 1, R = C2H5,
X-ray structure provided in Figure S7 in the SI) can be
Table 2. Select Bond Distances (Å) and Angles (deg) for
GADIPY
Ga1−N1
Ga1−Cl1
N2−Ga1−N1
N1−Ga1−Cl1
N1−Ga1−Cl2
1.898(2)
2.1694(5)
98.77(8)
113.46(3)
113.46(3)
Ga1−N2
Ga1−Cl2
N2−Ga1−Cl1
N2−Ga1−Cl2
Cl1−Ga1−Cl2
1.8949(19)
2.1694(5)
111.10(3)
111.10(3)
108.70(3)
B
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Journal of the American Chemical Society
Communication
than those of the other two chromophores, suggesting the
accessibility of different redox potentials for this heaver main
group BODIPY analogue. The calculations would suggest that
PHODIPY should have nearly identical λmax as the other two
chromophores shown in Figure 3. Stabilization of the ground
state by solvation (not reflected in these calculations) will be
more pronounced in cationic PHODIPY versus its neutral
analogues, accounting for both its higher Stokes shift and the
blue-shifted λmax
.
In conclusion, the current work has demonstrated a protocol
to access the first direct analogues of the widely explored
BODIPY chromophores in which heavier main group elements
are substituted for the borane. The strategy employed herein is
effective for generating neutral and cationic dipyrrin complexes
of group 3 and 5 elements, and should be readily extended to a
wide range of other heavier main group elements. Given the
wide range of N,N-chelating ligands and boron-containing
chromophores that have been reported,57−63 the facile method
reported herein should be applicable to a broad spectrum of
new chromophores beyond dipyrrin complexes as well. Efforts
are underway in our laboratory to prepare gallium complexes
of variously substituted dipyrrins to unveil their structure−
property relationships and to prepare isolable, kinetically
stabilized PHODIPY analogues.
Figure 2. UV−vis absorbance (solid lines) and photoluminescence
(PL, dotted lines) spectra for BODIPY (red), GADIPY (blue), and
PHODIPY (black) in dichloromethane.
weak photoluminescence upon excitation into the band at 511
nm. The PHODIPY λmax is blue-shifted, whereas the λem of
PHODIPY is red-shifted relative to the values for GADIPY and
BODIPY.
Density functional theory (DFT) calculations were
employed to gain a better understanding of the observed
photophysical properties of the three chromophores. The
calculated highest occupied molecular orbitals (HOMOs) and
lowest occupied molecular orbitals (LUMOs) and their
energies are provided for the three chromophores in Figure
3. Calculations reveal that both GADIPY and PHODIPY have
electron distributions in their HOMOs and LUMOs that are
very similar to those of BODIPY, despite the positive charge
on PHODIPY. The trigonal pyramidal geometry about P in
PHODIPY suggests that phosphorus P orbitals are not
involved in the π-conjugation or aromaticity of the system.
While the calculated bandgaps in vacuo for the three
chromophores are also quite similar at ∼3 eV (Table 1), the
energies of the HOMO and LUMO for GADIPY lie slightly
lower than those in BODIPY. HOMO and LUMO energies for
cationic PHODIPY of course lie significantly lower in energy
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.9b03235.
■
S
Synthetic procedures, analytical data, NMR spectra, and
additional photophysical data (PDF)
X-ray crystallographic data for GADIPY and EtGADIPY
(CIF)
AUTHOR INFORMATION
Corresponding Author
*rhett@clemson.edu
■
ORCID
Stephen E. Creager: 0000-0002-7412-2268
Figure 3. Ground state HOMO and LUMO distributions for GADIPY, BODIPY, and PHODIPY calculated by density functional theory at the
B3LYP-6-31G* level.
C
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Journal of the American Chemical Society
Communication
̈
(17) Vidal, F.; Jakle, F. Functional Polymeric Materials Based on
Main Group Elements. Angew. Chem., Int. Ed. 2019, 58, 5846.
Rhett C. Smith: 0000-0001-6087-8032
Notes
The authors declare no competing financial interest.
̈
(18) Alahmadi, A. F.; Lalancette, R. A.; Jakle, F. Highly Luminescent
Ladderized Fluorene Copolymers Based on B-N Lewis Pair
Functionalization. Macromol. Rapid Commun. 2018, 39 (22),
No. 1800456.
ACKNOWLEDGMENTS
■
(19) Wright, V. A.; Gates, D. P. Poly(p-phenylenephosphaalkene): A
Pi-Cojugated Macromolecule Containing P = C Bonds in the Main
Chain. Angew. Chem., Int. Ed. 2002, 41 (13), 2389−2392.
(20) Smith, R. C.; Protasiewicz, J. D. Conjugated Polymers
Featuring Heavier Main Group Element Multiple Bonds: A
Diphosphene-PPV. J. Am. Chem. Soc. 2004, 126 (8), 2268−2269.
(21) Cheng, Y.; Doyle, D. J.; Hitchcock, P. B.; Lappert, M. F. The β-
dialdiminato ligand [{N (C 6 H 3 Pr i 2−2, 6) C (H)} 2 CPh]: the
conjugate acid and Li, Al, Ga and In derivatives. Dalton Transactions
2006, No. 37, 4449−4460.
(22) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust,
J.; Noltemeyer, M.; Roesky, H. W. Synthesis and Characterization of
HC {C (Me) N (C6H3−2, 6-i-Pr2)} 2MX2 (M= Al, X= Cl, I; M=
Ga, In, X= Me, Cl, I): Sterically Encumbered β-Diketiminate Group
13 Metal Derivatives. Inorg. Chem. 2001, 40 (12), 2794−2799.
(23) Ito, S.; Hirose, A.; Yamaguchi, M.; Tanaka, K.; Chujo, Y. Size-
discrimination of volatile organic compounds utilizing gallium
diiminate by luminescent chromism of crystallization-induced
emission via encapsulation-triggered crystal−crystal transition. J.
Mater. Chem. C 2016, 4 (24), 5564−5571.
(24) Kuhn, N.; Fahl, J.; Fuchs, S.; Steimann, M.; Henkel, G.;
Maulitz, A. H. Vinamidin-Chelate des Aluminiums und Galliums. Z.
Anorg. Allg. Chem. 1999, 625 (12), 2108−2114.
(25) Stork, J. R.; Thoi, V. S.; Cohen, S. M. Rare Examples of
Transition-Metal-Main-Group Metal Heterometallic Metal-Organic
Frameworks from Gallium and Indium Dipyrrinato Complexes and
Silver Salts: Synthesis and Framework Variability. Inorg. Chem. 2007,
46 (26), 11213−11223.
(26) Thoi, V. S.; Stork, J. R.; Magde, D.; Cohen, S. M. Luminescent
Dipyrrinato Complexes of Trivalent Group 13 Metal Ions. Inorg.
Chem. 2006, 45 (26), 10688−10697.
(27) Lundrigan, T.; Baker, A. E. G.; Longobardi, L. E.; Wood, T. E.;
Smithen, D. A.; Crawford, S. M.; Cameron, T. S.; Thompson, A. An
Improved Method for the Synthesis of F-BODIPYs from Dipyrrins
and Bis(dipyrrin)s. Org. Lett. 2012, 14 (8), 2158−2161.
(28) Luyt, L. G.; Katzenellenbogen, J. A. A Trithiolate Tripodal
Bifunctional Ligand for the Radiolabeling of Peptides with Gallium-
(III). Bioconjugate Chem. 2002, 13 (5), 1140−1145.
The authors thank the NSF (CHE-0847132) for support.
REFERENCES
■
(1) Shah, M.; Thangaraj, K.; Soong, M.-L.; Wolford, L. T.; Boyer, J.
H.; Politzer, I. R.; Pavlopoulos, T. G. Pyrromethene−BF2 complexes
as laser dyes:1. Heteroat. Chem. 1990, 1 (5), 389−399.
(2) Baudron, S. A. Luminescent dipyrrin based metal complexes.
Dalton Transactions 2013, 42 (21), 7498−7509.
(3) Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Yu, L.; Bocian, D. F.;
Lindsey, J. S.; Holten, D. Structural control of the excited-state
dynamics of bis (dipyrrinato) zinc complexes: self-assembling
chromophores for light-harvesting architectures. J. Am. Chem. Soc.
2004, 126 (9), 2664−2665.
(4) Kusaka, S.; Sakamoto, R.; Kitagawa, Y.; Okumura, M.; Nishihara,
H. An Extremely Bright Heteroleptic Bis(dipyrrinato)zinc(II)
Complex. Chem. - Asian J. 2012, 7 (5), 907−910.
(5) Yang, L.; Zhang, Y.; Yang, G.; Chen, Q.; Ma, J. S. Zn(II) and
Co(II) mediated self-assembly of bis(dipyrrin) ligands with a
methylene spacer bridged at 3,3′-positions and their optical
properties. Dyes Pigm. 2004, 62 (1), 27−33.
(6) Filatov, M. A.; Lebedev, A. Y.; Mukhin, S. N.; Vinogradov, S. A.;
Cheprakov, A. V. π-Extended Dipyrrins Capable of Highly
Fluorogenic Complexation with Metal Ions. J. Am. Chem. Soc. 2010,
132 (28), 9552−9554.
(7) Ishida, M.; Naruta, Y.; Tani, F. A Porphyrin-Related Macrocycle
with an Embedded 1,10-Phenanthroline Moiety: Fluorescent
Magnesium(II) Ion Sensor. Angew. Chem., Int. Ed. 2010, 49 (1),
91−94.
(8) Ishida, M.; Lim, J. M.; Lee, B. S.; Tani, F.; Sessler, J. L.; Kim, D.;
Naruta, Y. Photophysical Analysis of 1,10-Phenanthroline-Embedded
Porphyrin Analogues and Their Magnesium(II) Complexes. Chem. -
Eur. J. 2012, 18 (45), 14329−14341.
(9) Hanson, K.; Tamayo, A.; Diev, V. V.; Whited, M. T.; Djurovich,
P. I.; Thompson, M. E. Efficient Dipyrrin-Centered Phosphorescence
at Room Temperature from Bis-Cyclometalated Iridium(III)
Dipyrrinato Complexes. Inorg. Chem. 2010, 49 (13), 6077−6084.
(10) Liu, X.; Nan, H.; Sun, W.; Zhang, Q.; Zhan, M.; Zou, L.; Xie,
Z.; Li, X.; Lu, C.; Cheng, Y. Synthesis and characterisation of neutral
mononuclear cuprous complexes based on dipyrrin derivatives and
phosphine mixed-ligands. Dalton Transactions 2012, 41 (34), 10199−
10210.
(11) Ikeda, C.; Ueda, S.; Nabeshima, T. Aluminium complexes of
N2O2-type dipyrrins: the first hetero-multinuclear complexes of
metallo-dipyrrins with high fluorescencequantum yields. Chem.
Commun. 2009, No. 18, 2544−2546.
(12) Jiang, X.-D.; Zhao, J.; Xi, D.; Yu, H.; Guan, J.; Li, S.; Sun, C.-L.;
Xiao, L.-J. A New Water-Soluble Phosphorus-Dipyrromethene and
Phosphorus-Azadipyrromethene Dye: PODIPY/aza-PODIPY. Chem. -
Eur. J. 2015, 21 (16), 6079−6082.
(13) Fihey, A.; Favennec, A.; Le Guennic, B.; Jacquemin, D.
Investigating the properties of PODIPYs (phosphorus-dipyrrome-
thene) with ab initio tools. Phys. Chem. Chem. Phys. 2016, 18 (14),
9358−9366.
(14) Kobayashi, J.; Kushida, T.; Kawashima, T. Synthesis and
Reversible Control of the Fluorescent Properties of a Divalent Tin
Dipyrromethene. J. Am. Chem. Soc. 2009, 131 (31), 10836−10837.
(15) Crawford, S. M.; Al-Sheikh Ali, A.; Cameron, T. S.; Thompson,
A. Synthesis and Characterization of Fluorescent Pyrrolyldipyrrinato
Sn(IV) Complexes. Inorg. Chem. 2011, 50 (17), 8207−8213.
(16) Y. Ren, F. J. In Main Group Strategies towards Functional Hybrid
(29) Cusnir, R.; Imberti, C.; Hider, C. R.; Blower, J. P.; Ma, T. M.
Hydroxypyridinone Chelators: From Iron Scavenging to Radiophar-
maceuticals for PET Imaging with Gallium-68. Int. J. Mol. Sci. 2017,
18 (1), 116.
(30) Bandoli, G.; Dolmella, A.; Tisato, F.; Porchia, M.; Refosco, F.
Mononuclear six-coordinated Ga(III) complexes: A comprehensive
survey. Coord. Chem. Rev. 2009, 253 (1), 56−77.
̌
̌
(31) Notni, J.; Simecek, J.; Hermann, P.; Wester, H.-J. TRAP, a
Powerful and Versatile Framework for Gallium-68 Radiopharmaceu-
ticals. Chem. - Eur. J. 2011, 17 (52), 14718−14722.
̈
(32) Velikyan, I.; Beyer, G. J.; Långstrom, B. Microwave-Supported
Preparation of 68Ga Bioconjugates with High Specific Radioactivity.
Bioconjugate Chem. 2004, 15 (3), 554−560.
(33) Berry, D. J.; Ma, Y.; Ballinger, J. R.; Tavare, R.; Koers, A.;
Sunassee, K.; Zhou, T.; Nawaz, S.; Mullen, G. E. D.; Hider, R. C.;
Blower, P. J. Efficient bifunctional gallium-68 chelators for positron
emission tomography: tris(hydroxypyridinone) ligands. Chem.
Commun. 2011, 47 (25), 7068−7070.
(34) Guo, H.; Yang, J.; Shenoy, N.; Miao, Y. Gallium-67-Labeled
Lactam Bridge-Cyclized α-Melanocyte Stimulating Hormone Peptide
for Primary and Metastatic Melanoma Imaging. Bioconjugate Chem.
2009, 20 (12), 2356−2363.
(35) Summer, D.; Grossrubatscher, L.; Petrik, M.; Michalcikova, T.;
Novy, Z.; Rangger, C.; Klingler, M.; Haas, H.; Kaeopookum, P.; von
Guggenberg, E.; Haubner, R.; Decristoforo, C. Developing Targeted
̈
Materials; Baumgartner, T., Jakle, F., Eds.; John Wiley & Sons Ltd.:
Chichester, 2018; pp 79−110.
D
DOI: 10.1021/jacs.9b03235
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
Hybrid Imaging Probes by Chelator Scaffolding. Bioconjugate Chem.
2017, 28 (6), 1722−1733.
(36) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J.
Phosphine Coordination Complexes of the Diphenylphosphenium
Cation: A Versatile Synthetic Methodology for P-P Bond Formation.
J. Am. Chem. Soc. 2003, 125 (47), 14404−14410.
(37) Duvva, N.; Sudhakar, K.; Badgurjar, D.; Chitta, R.; Giribabu, L.
Spacer controlled photo-induced intramolecular electron transfer in a
series of phenothiazine-boron dipyrromethene donor-acceptor dyads.
J. Photochem. Photobiol., A 2015, 312, 8−19.
(38) Hoye, A. T.; Davoren, J. E.; Wipf, P.; Fink, M. P.; Kagan, V. E.
Targeting mitochondria. Acc. Chem. Res. 2008, 41 (1), 87−97.
(39) Smith, R. A. J.; Porteous, C. M.; Gane, A. M.; Murphy, M. P.
Delivery of bioactive molecules to mitochondria in vivo. Proc. Natl.
Acad. Sci. U. S. A. 2003, 100 (9), 5407−5412.
(56) Smith, R. C.; Earl, M. J.; Protasiewicz, J. D. Synthesis and
photoluminescent properties of a series of pnictogen-centered
chromophores. Inorg. Chim. Acta 2004, 357 (14), 4139−4143.
(57) Cassidy, S. J.; Brettell-Adams, I.; McNamara, L. E.; Smith, M.
F.; Bautista, M.; Cao, H.; Vasiliu, M.; Gerlach, D. L.; Qu, F.; Hammer,
N. I.; Dixon, D. A.; Rupar, P. A. Boranes with Ultra-High Stokes Shift
Fluorescence. Organometallics 2018, 37 (21), 3732−3741.
(58) Cao, H.; Bauer, N.; Bi, S.; Li, D.; You, W.; Rupar, P. A. Post-
polymerization modification of phosphorus containing conjugated
copolymers. Eur. Polym. J. 2018, 104, 157−163.
(59) Cao, H.; Brettell-Adams, I. A.; Qu, F.; Rupar, P. A. Bridged
difurans: stabilizing furan with p-block elements. Organometallics
2017, 36 (14), 2565−2572.
(60) Tanaka, K.; Chujo, Y. Advanced luminescent materials based
on organoboron polymers. Macromol. Rapid Commun. 2012, 33 (15),
1235−55.
(61) Tamgho, I.-S.; Hasheminasab, A.; Engle, J. T.; Nemykin, V. N.;
Ziegler, C. J. A New Highly Fluorescent and Symmetric Pyrrole-BF2
Chromophore: BOPHY. J. Am. Chem. Soc. 2014, 136 (15), 5623−
5626.
(40) Tan, X.; Luo, S.; Long, L.; Wang, Y.; Wang, D.; Fang, S.;
Ouyang, Q.; Su, Y.; Cheng, T.; Shi, C. Structure-Guided Design and
Synthesis of a Mitochondria-Targeting Near-Infrared Fluorophore
with Multimodal Therapeutic Activities. Adv. Mater. (Weinheim, Ger.)
2017, 29 (43), 1704196.
(62) Rhoda, H. M.; Chanawanno, K.; King, A. J.; Zatsikha, Y. V.;
Ziegler, C. J.; Nemykin, V. N. Unusually Strong Long-Distance Metal-
Metal Coupling in Bis(ferrocene)-Containing BOPHY: An Introduc-
tion to Organometallic BOPHYs. Chem. - Eur. J. 2015, 21 (50),
18043−18046.
(63) Zatsikha, Y. V.; Nemez, D. B.; Davis, R. L.; Singh, S.; Herbert,
D. E.; King, A. J.; Ziegler, C. J.; Nemykin, V. N. Testing the Limits of
the BOPHY Platform: Preparation, Characterization, and Theoretical
Modeling of BOPHYs and Organometallic BOPHYs with Electron-
Withdrawing Groups at β-Pyrrolic and Bridging Positions. Chem. -
Eur. J. 2017, 23 (59), 14786−14796.
(41) Yoshifuji, M. Product class 3: phosphenium salts. Sci. Syn. 2009,
42, 63−69.
(42) Hering, C.; Schulz, A.; Villinger, A. Low-Temperature Isolation
of An Azidophosphenium Cation. Angew. Chem., Int. Ed. 2012, 51
(25), 6241−6245.
(43) Weigand, J. J.; Burford, N.; Lumsden, M. D.; Decken, A. A melt
approach to the synthesis of catena-phosphorus dications to access
derivatives of [P6Ph4R4]2+. Angew. Chem., Int. Ed. 2006, 45 (40),
6733−6737.
(44) Spinney, H. A.; Korobkov, I.; DiLabio, G. A.; Yap, G. P. A.;
Richeson, D. S. Diamidonaphthalene-Stabilized N-Heterocyclic
Pnictogenium Cations and Their Cation-Cation Solid-State Inter-
actions. Organometallics 2007, 26 (20), 4972−4982.
(45) Dahl, O. Reactions of aminophosphines with trifluorometha-
nesulfonic acid: phosphenium ion (two-coordinate phosphorus ion)
or tricovalent phosphorus products? Tetrahedron Lett. 1982, 23 (14),
1493−6.
(46) Cowley, A. H.; Kemp, R. A. Synthesis and reaction chemistry of
stable two-coordinate phosphorus cations (phosphenium ions). Chem.
Rev. 1985, 85 (5), 367−82.
(47) Burford, N.; Clyburne, J. A. C.; Bakshi, P. K.; Cameron, T. S.
η6-Arene complexation to a phosphenium cation. J. Am. Chem. Soc.
1993, 115 (19), 8829−30.
(48) Carmalt, C. J.; Lomeli, V. Cyclic phosphenium and arsenium
cations with 6π electrons and related systems. Chem. Commun.
(Cambridge, U. K.) 1997, No. 21, 2095−2096.
(49) Burck, S.; Gudat, D.; Nieger, M.; Du Mont, W.-W. P-
Hydrogen-Substituted 1,3,2-Diazaphospholenes: Molecular Hydrides.
J. Am. Chem. Soc. 2006, 128 (12), 3946−3955.
(50) Vidovic, D.; Lu, Z.; Reeske, G.; Moore, J. A.; Cowley, A. H. An
N,N’-chelated phosphenium cation supported by a β-diketiminate
ligand. Chem. Commun. (Cambridge, U. K.) 2006, No. 33, 3501−3503.
(51) Renard, S. L.; Kee, T. P. Electronic effects on the acidity of
phosphorus(III) triflates. J. Organomet. Chem. 2002, 643−644, 516−
521.
(52) Yang, Y.; Liu, Z.; Liu, B.; Duchateau, R. Selective Ethylene
Tri-/Tetramerization by in Situ-Formed Chromium Catalysts
Stabilized by N,P-Based Ancillary Ligand Systems. ACS Catal. 2013,
3 (10), 2353−2361.
(53) Zhu, G.; Li, X.; Xu, G.; Wang, L.; Sun, H. A new PC(sp3)P
ligand and its coordination chemistry with low-valent iron, cobalt and
nickel complexes. Dalton Transactions 2014, 43 (23), 8595−8598.
(54) Smith, R. C.; Chen, X.; Protasiewicz, J. D. A Fluorescent (E)-
Poly(p-phenylenephosphaalkene) Prepared by a Phospha-Wittig
Reaction. Inorg. Chem. 2003, 42 (18), 5468−5470.
(55) Smith, R. C.; Protasiewicz, J. D. Synthesis and luminescence
properties of a series of tris(4-styrylphenyl)phosphorus-(III) and -(V)
compounds and of a [Cu(PR3)4]BF4 complex. Dalton Transactions
2003, No. 24, 4738−4741.
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DOI: 10.1021/jacs.9b03235
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX